The present invention relates generally to valves for controlling the flow of fluids and particulate solid materials and relates more particularly to a pinch type valve of the full round type adapted to close and lock to a leak tight condition even with line pressures in the range of 400 psig.
Pinch type valves have been widely employed to control the flow of such diverse products as dry, abrasive and granular materials and corrosive fluids. The popularity of this type of valve stems from its simplicity, smooth-walled flow path, ability to govern flows of fluid, solid or mixed solid and fluid materials, and adaptability for remote operation. Pinch valves may be built in practically any required size, and require little or no maintenance.
A pinch type valve as the name implies comprises a generally cylindrical hollow elastomeric sleeve known as the valve body, which when pinched between its ends, restricts or stops flow through the body. The pinching of the valve is usually accomplished by mechanical means comprising a pair of opposed pinch bars, one or both of which may be movable.
There are two basic types of pinch valves currently manufactured, the full round opening type wherein the pinched portion of the valve opens to the same cross-sectional size and shape as the ends of the valve body, and the pre-pinched type usually characterized by a fixed pinch bar which holds one side of the valve body in a flattened condition. The pre-pinched type suffers the disadvantage of a constriction in the size of the fluid passage which may become clogged if large objects are to be carried through the valve. The advantages of the pre-pinched type include a simpler actuating mechanism and a shorter actuator stroke with the flow rate more closely corresponding to the displacement of the actuator.
The disadvantages of the conventional full round opening type pinch valve are the long actuator stroke required to close the valve, the complicated actuator mechanism and the inherently non-linear flow characteristics. The first 50% of actuator movement on closure of the conventional valve produces very little change in the flow rate. As a result, most of the valve closure takes place during the past portion of the actuator movement with about 50% of the closure occurring during the last 20% of the actuator movement. Since the closing force required to close a pinch valve increases as the valve approaches the closed position, it can be understood that a conventional valve actuator would require an extremely high actuating force to operate a full round opening type pinch valve under high fluid pressure conditions.
In my U.S. Pat. No. 3,734,133, issued May 22, 1973, a pinch valve actuating mechanism is disclosed which overcomes a number of the problems associated with full opening valves. The actuator of that patent is related to the present invention in that valve closure from full open to full closed is effected by only a 90.degree. rotation of the drive shaft, and the actuator linkage provides an increasing mechanical advantage as the valve approaches the closed position. However, the valve of the patent will only lock against line pressure from one direction, and because of the arcuate movement of one of the pinch bars, cannot be made positive opening from both sides. Furthermore the rolling movement of one of the pinch bars along the valve body produces a considerable frictional resistance which must be overcome by the actuator.